1. Field of the Invention
The present invention relates to a duct type air conditioner and a method of controlling the same and, more particularly, to a supply temperature constant control method.
2. Description of the Related Art
In buildings and the like having a large number of rooms, a duct type air conditioner is adopted to distribute temperature-adjusted air to each room by using an air duct, thereby performing air conditioning. In recent years, as multi-purpose tenant buildings and the like are increased in number, a demand has increasingly arisen for a subdividing air conditioning system capable of adjusting a temperature or switching operations in accordance with an area or purpose of each room. Therefore, various improvements have been made in the duct type air conditioner in order to cope with such a demand As one of such improvements, a control method using a variable air volume control scheme (to be referred to as a VAV scheme hereinafter) as disclosed in Published Unexamined Japanese Patent Application No. 62-37632 or 62-194159 has been adapted. In this VAV scheme, the opening of a damper provided at a supply opening of each room is adjusted in accordance with the temperature of the room, and a supply air volume of a fan is controlled in accordance with a static pressure of an air circulating system which changes in accordance with the damper opening. In this manner, temperature control is performed by changing the air volume. In addition, a compressor is ON/OFF-controlled in accordance with a cooling/heating load (the number of rooms) independently of the air volume control.
FIG. 1 is a timing chart showing characteristics obtained when a duct type air conditioner adopting the above VAV scheme is applied to, e.g., four rooms. As can be understood from FIG. 1, during a high cooling/heating load (four rooms) operation, a room temperature T.sub.a can be substantially set at a set room temperature T.sub.s. During a low cooling/heating load (one room) operation, however, the room temperature T.sub.a largely varies with respect to the set room temperature T.sub.s since a compressor is ON/OFF-controlled. That is, when the conventional duct type air conditioner is used, a room temperature largely varies during the low cooling/heating load operation. In addition, since the opening of the damper is decreased during the low cooling/heating load operation, a duct pressure loss is increased to result in high operation noise.
In the conventional duct type air conditioner, a wind pressure is detected by a pressure sensor. Therefore, since only an average air volume to be supplied to each room can be detected, a required air volume cannot be supplied.
Recently, a duct type air conditioner which adopts compressor inverter control in addition to the above VAV scheme has been developed as disclosed in Published Unexamined Japanese Patent Application No. 62-22948. In such an air conditioner, however, since the frequency of an inverter for driving a compressor is selected in accordance with the opening of a damper, the opening of the damper and the frequency of the inverter cannot be controlled independently of each other. That is, when the damper opening is increased in order to decrease a duct pressure loss, the frequency of the inverter is also increased to consume unnecessarily high cooling/ heating power. Therefore, since the opening of the damper is decreased so as not to consume the unnecessarily high cooling/heating power during a low cooling/heating load operation, the duct pressure loss is increased as described above to result in high operation noise.